1. Field of the Invention
The present invention is directed to providing nonmetallic cured resins and composites with a conductive metal surface, and more particularly, to preparing the surface of a cured cyanate ester resin or composite for plating with metal.
2. Description of Related Art
Metals are commonly employed in manufacturing because they offer high degrees of ductility and strength as well as high conductivity. However, metals are generally heavier than other common materials like plastics, such that the positive characteristics attributable to metals often come at the cost of increased product weight. Increased product weight is particularly a concern in industries manufacturing vehicles of transport such as automobiles, aircraft, and spacecraft, as well as payloads of such vehicles, given that increased weight adversely affects fuel economy. Accordingly, these industries have increasingly incorporated non-metallic, lighter-weight materials such as plastics into automobiles and aircraft in an effort to economize fuel.
However, plastics are not universally suitable as substitutes for metals. For example, while plastics offer high degrees of ductility and strength, plastics are relatively nonconductive materials. Thus, plastics cannot supplant metals used as electrical, thermal, or microwave conductors.
It would be desirable to plate a metal coating onto nonmetallic plastic, thereby simultaneously realizing the benefits of both metals and plastics. More specifically, metal plating on such commonly-used plastic materials as cured cyanate ester resins and composites would allow the use of these lighter-weight plastic materials for the bulk of components and would minimize the amount of metal required to achieve a highly conductive surface. However, plating metal onto many untreated plastic surfaces has been unsuccessful because these materials do not inherently adhere to one another.
There are methods available to improve the adhesion between metals and certain nonmetallic surfaces. One such process, commercially available from Shipley Chemicals, employs a series of treatment baths to clean, texturize, neutralize, condition, and etch the resin surfaces of circuit board composites in preparation for electroless copper processing. For example, the Shipley process employs an alkaline permanganate bath to texturize the resin surface and a persulfate-based micro-etch system to promote adhesion of the copper to the resin surface. While the Shipley process presumably improves the adhesiveness between copper and the surfaces of circuit boards, its multiple steps and numerous chemical compounds are cumbersome.
We have found that plating of metal coatings onto cyanate ester polymers and reinforced composites made with these polymers is particularly difficult. The previously described methods for plating metals on other polymers do not work satisfactorily for the cyanate ester polymers and their composites. A new and improved method for plating these materials would be very valuable, because the cyanate ester polymers and their composites have certain unique advantages that make them very useful for specific applications, such as applications in communications spacecraft. These polymers and composites can be formulated in ways that make them very resistant to even minute dimensional changes that would otherwise occur as a result of temperature changes or the absorption and desorption of moisture in the presence of air. Since these applications also require that the surface of these articles also have a high electrical conductivity, it is very useful and important to provide a method for plating metals on these plastics and composites.
Thus, a need remains for a method to improve adhesion of a metal coating to cured cyanate ester resins and composites. The method should consist of a minimal number of steps so that production rates may be optimized. The present invention fulfills these needs.